Although glass is the most common transparent material used in buildings, vehicles, and the like, glass is not acceptable for all such applications. Glass is relatively heavy and brittle, and may shatter into a multiplicity of sharp parts when impacted. These properties make glass disadvantageous for many applications, including some building and vehicle windows. Additionally, glass is difficult to form into complex shapes.
For many applications in which the potential for impact or other strains and/or stresses exist, there exists a general need for mechanically strong composite materials that are of high optical quality and have an optical transparency similar or equivalent to that of glass. Polymers such as polymethylmethacrylate (PMMA), sold under the trademark PLEXIGLASS, are used in place of glass in certain applications in which both impact resistance and optical transparency are required. Unfortunately, thermoplastic polymers such as PMMA still do not have sufficient mechanical strength for many current applications.
One method of increasing the mechanical strength of polymers like PMMA is to reinforce them with strong glass fibers. This technology is practiced in the manufacture of fiberglass-reinforced plastics (FRP). In most cases, however, the introduction of glass fibers into an optically transparent polymer limits or destroys the transparency of the polymer. Commercial FRP composites presently produced are either optically opaque or translucent such that an object at distances greater than about a few feet cannot be clearly seen through them, and/or significant distortions occur.
Among the problems that exist in the aforesaid glass fiber/thermoplastic polymer composites is that changes in the temperature of such composites can cause the relative refractive indices of the glass fibers and polymer to change relative to one another such that they become mismatched. While the impact resistance of a thermoplastic polymer may be better than that of glass, its strength is lower. The stiffness of the thermoplastic polymer can also be undesirable for some applications. Finally, the thermoplastic polymer tends to degrade quickly with increasing temperature. This mismatching results in degraded composite clarity and/or transparency. This lack of clarity with temperature change means that glass fiber-reinforced transparent composites lose clarity when used in anything except for a narrow range of temperatures. Also, even within a limited temperature range, the clarity of glass fiber-reinforced composites may be noticeably less than that of glass. This is unacceptable for applications such as use for home or building windows.
As a result of these and other problems, unresolved needs remain in the art.